I have had a z411-48 with a 2 cylinder Kawasaki for a few years. I presume that the 412 is the newer version. In general I like it a lot, but it does tend to slide on hills, either when the grass is wet, or when I'm running over grass I just cut. I have thought about going to more aggressive atv tires, but I can't find a match for the uncommon tire size that came stock on the machine. I feel that filling the tires wouldn't necessarily be a remedy, but I have no evidence to support that view.
As for bouncy ride, I did add the Kubota cushion seat mount. It made a difference, but it still bounces me around some.